Honestly, if you bother to understand what it is that terrorist organizations are trying to do, what they're attempting to achieve, the base they're playing to, who they're attempting to influence--you would realize they have NOTHING to gain by setting wildfires in random areas. Terrorist groups have no real desire to, nor can they, inflict serious economic damage on a large scale to major nations. And even if they could, forest fires aren't the way to do it.

Terrorist groups that want to become major players have a strategy, honed by Mao and to a lesser extent the Viet Minh: first create a solid base among your target nation, then establish a shadow government among the base, then destabilize the local government in the target nation(the place where most insurgencies collapse), THEN destabilize the national government. Almost nobody ever gets beyond step three, for obvious reasons. Setting big fires in a region, unless that area is solely dependent on timber exports, isn't going to do much more than annoy the local residents and probably kill your base.

Just another example of the local politicians trying to use terrorists as a means to tighten their own grip on the populace, I'd imagine.